Gallium nitride (GaN) offers substantial opportunity to enhance performance of electronic devices such as high electron mobility transistors (HEMTs). In general, a GaN HEMT has a Schottky layer and a GaN buffer layer deposited on a substrate and source, gate, and drain contacts deposited on the Schottky layer. However, during high voltage/power operation, electrons may gain enough kinetic energy to be injected into the substrate, thereby degrading the performance of the HEMT.
In addition, the Schottky layer is typically metallic and may be exposed to air during fabrication of the HEMT and/or during operation of the HEMT. By exposing the Schottky layer to air, surface reactions such as oxidation may occur on the surface of the Schottky layer. These surface reactions may degrade the performance of the HEMT and also decrease the effectiveness of passivation. Passivation is the deposition of a dielectric material on the surface of the HEMT in order to passivate, or fill, surface traps on the surface of the HEMT, thereby avoiding device degradation due to these surface traps such as RF to DC dispersion.
Therefore, there remains a need for a high voltage GaN HEMT structure. In addition, there remains a need for a GaN HEMT having a reproducible termination layer capable of preventing surface reactions during fabrication and operation of the GaN HEMT.